Optimal PSI for 315/30ZR22? Michelin Pilot Sport 4s

[funclub@caseyha]

Anyone running tires this size on a c8? I'm new to cars like this and I'm having a real hard time figuring out the correct psi for proper contact patch and performance

I have the car stage 3 tuned and swapped to 315s so I have the ability to put the power down better

Been chalking and experimenting a ton to dial this stuff in but based on everything I am reading vs what I am seeing in application is confusing me a lot

Based on the tire calculator for psi, shaping from the stock 285s to 315 on a 22 wheel I should be sitting at 35 psi hot, but when chalk the tires and test contact patch is almost seems like I have to drop the psi to 23 or 24psi hot to get the entire shoulder of the tire to heat up evenly with the middle

This is setting off all the flat tire warnings on the car, even after I reset the tire pressure in the MMI

My goal is to get the car in the optimal range to pit power down in corners while not losing much on launches

Cornering and wet handling are my main focus for safety. Don't want to roll over on the side walls

The TPMS throwing flat tire warnings all the time is pretty concerning and I'm starting to wonder if I'm looking at the wrong part of the tires shoulder and should be focusing in a point higher up on the tire

[OneFastBMW]

That seems VERY low for a 30 aspect tire. You can likely tell from the wear on the shoulders how much you are “rolling over” on the tire in turns, but I would think you’re not too far from rolling off the bead. These are HEAVY cars, I have seen people look for equal temp across the entire tire cross section on a drag car, but not a street car.

Just out of curiosity, what calculator are you using that says 35 hot? With the factory 22’s Audi recommends 47psi for the 190mph top speed.

[tinmanwpk]

I would start with the factory recommended specs as mentioned in your manual, not the driver side door sticker. I would tweak it from there.

[Jprieur]

I am shocked that size tire clears lock to lock, no rubbing at full lock???

[KRS Aaron]

I am shocked that size tire clears lock to lock, no rubbing at full lock???

I have been lurking on this post with this same thought. Can't imagine how it doesn't cause other issues with that size. In my racing experience, there is such thing as too much tire and a fine balance on width and overall size versus handling capabilities. A personal example is using 275 vs. 295 tires on my race car at Road America. Its a 4-5 mph difference on the straights with the 275 and no loss of cornering speed or braking ability. This tells me the 295 is too much tire for that track but I do run the 295 at other tracks where there may be only one crucial straight or some fast cornering I need the extra beef for.

[carguyshu]

That seems VERY low for a 30 aspect tire. You can likely tell from the wear on the shoulders how much you are “rolling over” on the tire in turns, but I would think you’re not too far from rolling off the bead. These are HEAVY cars, I have seen people look for equal temp across the entire tire cross section on a drag car, but not a street car.

Just out of curiosity, what calculator are you using that says 35 hot? With the factory 22’s Audi recommends 47psi for the 190mph top speed.

Keep in mind that recommended PSI for top speed is totally different compared to maximizing grip. With the PS4 on almost any car you want whatever the recommended cold PSI is at your target hot PSI. On my blackwing, for instance, 35psi is the recommended cold tire pressure for street driving. However when track driving I have to take them down to 28psi at the beginning of the session. They grip the most warm between 34-36psi. This is on a modified PS4 designed specifically for the blackwing. If you air down to 28psi you're not going to get good grip and the car will feel spongy until you get the tires up to temp and warm. At least on that car (and on most others) once you get into the 38-40 psi range they tend to have the outer shoulder come off in chunks when pushing hard at the track. Hope this info helps.

[rusq5]

I am shocked that size tire clears lock to lock, no rubbing at full lock???

hoping for an answer on this as well. really disappointed the 305 PSS was discontinued.

[funclub@caseyha]

hoping for an answer on this as well. really disappointed the 305 PSS was discontinued.

They clear lock to lock on 22" wheels, there was only about a cm or two of room on the fender at full lock on the horizontal x axis

Interestingly, lowering the car gave a bit more space cause of how the fender is shaped

If you're at VIR audi event next weekend you're welcome to come check the car out

[funclub@caseyha]

https://tiresize.com/pressure-calculator/

The calculator goes off load rating at various psi

If I'm running the 155 mph speed psi ratings then thst calculator puts the fronts at 30psi and rear at 29 psi

That's supposed to be cold psi, but like someone said the pss4 likes to run lower psi when warmed up

after more playing around it seems like the 315 handles well on the street for me at 30 psi cold, 32 psi warm all round. I'm running drc with rear steering and an upgraded sway bar

I'll play around with it more on track next weekend and see how it handles and what the wear looks like near the sidewalls

[Kolbaskin]

Hi,
In my opinion 295/30 is enough for 9.9s on 1/4. I'm using Conti 7 on this size and love it. Fastest C8 so far)

[funclub@caseyha]

Hi,
In my opinion 295/30 is enough for 9.9s on 1/4. I'm using Conti 7 on this size and love it. Fastest C8 so far)

congrats on the time

Swapping from 285 to 315 stopped my tires from spinning on launches but maybe I just needed to go up to 295s

Your 0-100 seems to be 0.2s slower than what power division and brex put down with their cars recently though

Maybe you didn't hookup as quick and made up for it in the second half?

My car has rear wheel steering so I'm never going to match you guys on those times. Which turbos did you go with on your tune?

[Jprieur]

Any pics of those tires on the rim? Curious how it looks compared to the 'stretch' look of the stock 285

[Kolbaskin]

Hi,
I can't find any dragy times made by brex or power division promising 2.4 sec 0-100.
I'm LM990 turbos.
PS all rs6 has rear wheel steering.

[RMode]

congrats on the time

Swapping from 285 to 315 stopped my tires from spinning on launches but maybe I just needed to go up to 295s

Your 0-100 seems to be 0.2s slower than what power division and brex put down with their cars recently though

Maybe you didn't hookup as quick and made up for it in the second half?

My car has rear wheel steering so I'm never going to match you guys on those times. Which turbos did you go with on your tune?

comparing draggy results from one car to another, one day to another, is borderline useless. It's a useful took unto itself, on your car

[funclub@caseyha]

I don't understand this line of thought. If that were the case, it seems drag racing wouldn't even be a sport

We make mods to the cars and make them do things so we can show them off and talk about them. One of the more popular ones seems to be getting the same model car to go faster than the next guy and draggy is one of the more reliable ways to measure that

[funclub@caseyha]

Hi,
I can't find any dragy times made by brex or power division promising 2.4 sec 0-100.
I'm LM990 turbos.
PS all rs6 has rear wheel steering.

According to several tuners and automechanics I have worked with this year you can order a c8 rs7 / rs6 without rear wheel steering and a lot of the top draggys are being ran without the setup because it shaves approx 1200lbs off the curb weight of the car. If you're running a 9.88s 1/4 mile with rear wheel steering, more power to you cause that's crazy good. I wish I had more room around here to do test runs to see how the weather drop has improved my acceleration since tuning the car this summer but I don't get a chance to do it often
2.4s:

https://www.youtube.com/watch?v=rMsNyDdynIc

https://www.youtube.com/watch?v=CGuRXNMEYps

https://www.youtube.com/watch?v=ZMRBGiLXjUM

[suffeks]

rws option weighs 1200lbs? I call bullshit, prove it

[STALKER]

rws option weighs 1200lbs? I call bullshit, prove it

I agree.
These systems, at least the ones that aren’t turning the wheels 10+ degrees are not terribly complicated or large.

[suffeks]

here's your 1200lbs LOL

https://www.ebay.co.uk/itm/144000135298
https://www.ebay.com/itm/115713014576

[Jprieur]

1200 lbs would account for the engine, TWICE!!!!!!! lol

Also, you cannot order the C8 RS6/7 without rear wheel steering.

If you have tuners and mechanics telling you these things, find new versions of both! Fast!

[RMode]

I don't understand this line of thought. If that were the case, it seems drag racing wouldn't even be a sport

We make mods to the cars and make them do things so we can show them off and talk about them. One of the more popular ones seems to be getting the same model car to go faster than the next guy and draggy is one of the more reliable ways to measure that

Drag racing is a sport because cars compete, live, in person, at the same time, so the environment doesn’t offer an advantage. The only difference would be one lane vs another.

Perhaps that’s your motivation to modify- and that’s great. I promise you, it’s not everyone’s.


Sent from my iPhone using Tapatalk

[tinmanwpk]

I'm having a hard time with 1200 pounds as well. The two fleabay examples - I was unable to find the weight. Was it posted and I just had one Scotch too many? And how did we get this far off topic?

[funclub@caseyha]

1200 lbs would account for the engine, TWICE!!!!!!! lol

Also, you cannot order the C8 RS6/7 in this without rear wheel steering.

If you have tuners and mechanics telling you these things, find new versions of both! Fast!

All I know is what I'm told, I don't care enough about this stuff to look that deep into it

I've had one of the head engineers at Unitronic, and several mechanics at shops thst specialize in tuning audio ask me if it has rear wheel steering because you can get c8 models without. It's one of the first questions they ask when they start working on the car so they have the right info to measure the mods against

As far as the weight for the drive system itself, I got the 1200lb number from the engineer at unitronic and had a mechanic independently mention approximately the same weight amount at a different date

[funclub@caseyha]

Drag racing is a sport because cars compete, live, in person, at the same time, so the environment doesnÂ’t offer an advantage. The only difference would be one lane vs another.

Perhaps thatÂ’s your motivation to modify- and thatÂ’s great. I promise you, itÂ’s not everyoneÂ’s.


Sent from my iPhone using Tapatalk

Doesn't change the fact that people tinker with their cars so they car do things like go faster than the next guy

Also, my comment wasn't just about drag strips, it was just one example. I wasn't even they guy that started posting dragys in the thread

People mod their cars so they can be proud of them and show them off

This whole thread was supposed to be about figuring out the optimal psi for aftermarket tires so the car could corner well without giving up too much traction from a dig. It was never about running a 1/4 in world record time or anything else of the sort

295s might let the car run faster than 315s, so what? So do 20s vs 22s because of the unsprung and rotational weight reduction

I run 22s and 315s because I think they look a hell of a lot cooler on the car for how wide the rear end is and the car still pulls respectable 0-60 numbers for a street car

having wide tires let's me stop a lot quicker too in the summer of I need to get on the brakes when someone does something silly around DC. People do wild shit here all the time at rush hour

[RMode]

Doesn't change the fact that people tinker with their cars so they car do things like go faster than the next guy

Also, my comment wasn't just about drag strips, it was just one example. I wasn't even they guy that started posting dragys in the thread

People mod their cars so they can be proud of them and show them off

This whole thread was supposed to be about figuring out the optimal psi for aftermarket tires so the car could corner well without giving up too much traction from a dig. It was never about running a 1/4 in world record time or anything else of the sort

295s might let the car run faster than 315s, so what? So do 20s vs 22s because of the unsprung and rotational weight reduction

I run 22s and 315s because I think they look a hell of a lot cooler on the car for how wide the rear end is and the car still pulls respectable 0-60 numbers for a street car

having wide tires let's me stop a lot quicker too in the summer of I need to get on the brakes when someone does something silly around DC. People do wild shit here all the time at rush hour

You're the one referencing other draggy results as some sort of measuring stick, without context. Such as each of the other places you quoted times for aren't based in the US in the first place. Makes for a very different animal when fuel differs a lot, just by itself.

You can't get an RS6 in the US without rear wheel steerring, from 2021-present. The rear rack and associated wiring and modules weigh maybe 200 lbs. For it to weigh 1200 lbs is insane, and would mean an RS6 without it, unladen, weighs less than a base A3. Which is not without the realm of reality. So perhaps you misheard what they said, or they are unsure of what they are actually saying.

Point of it all, the draggy is a neat tool - it's far from infallible as has been shown countless times, and it's single best point of reference is charting progressive changes to your car. Just like the Naturally people will then start to compare results, like they compare dynos, or other things that rely on context. Human nature...which only further reinforces that it's just an incorrect way of going about things. These sorts of things have existed in many forms for many years. I am sure many of us here remember the G Tech meters, or the PDA Dyno

have fun!

[funclub@caseyha]

You're the one referencing other draggy results as some sort of measuring stick, without context. Such as each of the other places you quoted times for aren't based in the US in the first place. Makes for a very different animal when fuel differs a lot, just by itself.

You can't get an RS6 in the US without rear wheel steerring, from 2021-present. The rear rack and associated wiring and modules weigh maybe 200 lbs. For it to weigh 1200 lbs is insane, and would mean an RS6 without it, unladen, weighs less than a base A3. Which is not without the realm of reality. So perhaps you misheard what they said, or they are unsure of what they are actually saying.

Point of it all, the draggy is a neat tool - it's far from infallible as has been shown countless times, and it's single best point of reference is charting progressive changes to your car. Just like the Naturally people will then start to compare results, like they compare dynos, or other things that rely on context. Human nature...which only further reinforces that it's just an incorrect way of going about things. These sorts of things have existed in many forms for many years. I am sure many of us here remember the G Tech meters, or the PDA Dyno

have fun!

Nah man, go back and read the thread again. I wasn't the one to start posting dragy runs

I made this thread to figure out optimal street PSI for after market wheels thst were bigger than stock for corner handling while not giving up much traction

I didn't bring up dragy until someone else decided to slide, post their dragy run, and talk about how 315s weren't needed and they seemed to be doing well on 295s

I couldn't care less about any of that stuff but it I happened to notice that even though the guy ran a 9s 1/4 mile his launch was slower than the other runs, which seems to indicate he doesn't have as much traction from a dig as the other guys and isn't hooking as fast

I also haven't misunderstood anything about the rear wheel steering weight. I've been working with unitronic all year on tuning my car. It's in my email, in writing

Whether those guys are right also isn't any of my concern

Don't move the goal post by changing it to non of the US models can be bought without the rear steering now. You said none of c8s at first, not just in the US

I'm running off the information I'm being given by all the guys that make a living tuning these cars, so if I've got any of my info wrong then that's on them, not me

I'm just here to make my car look nice and go fast, not set world records or measure my anatomy against anyone

So I'd prefer people get their act together and get back on topic or just gtfo of the thread at this point

Currently I've been running 39psi up front and 32psi in the back on my 315s to help combat some of the natural understeer. Car seems to be hooking relatively well from a dig and still has enough psi thst the city streets don't drag my be left and right to much on hard acceleration

still tinkering with different setups, if you have anything worthwhile to add to the discussion

[RMode]

Nah man, go back and read the thread again. I wasn't the one to start posting dragy runs

I made this thread to figure out optimal street PSI for after market wheels thst were bigger than stock for corner handling while not giving up much traction

I didn't bring up dragy until someone else decided to slide, post their dragy run, and talk about how 315s weren't needed and they seemed to be doing well on 295s

I couldn't care less about any of that stuff but it I happened to notice that even though the guy ran a 9s 1/4 mile his launch was slower than the other runs, which seems to indicate he doesn't have as much traction from a dig as the other guys and isn't hooking as fast

I also haven't misunderstood anything about the rear wheel steering weight. I've been working with unitronic all year on tuning my car. It's in my email, in writing

Whether those guys are right also isn't any of my concern

Don't move the goal post by changing it to non of the US models can be bought without the rear steering now. You said none of c8s at first, not just in the US

I'm running off the information I'm being given by all the guys that make a living tuning these cars, so if I've got any of my info wrong then that's on them, not me

I'm just here to make my car look nice and go fast, not set world records or measure my anatomy against anyone

So I'd prefer people get their act together and get back on topic or just gtfo of the thread at this point

Currently I've been running 39psi up front and 32psi in the back on my 315s to help combat some of the natural understeer. Car seems to be hooking relatively well from a dig and still has enough psi thst the city streets don't drag my be left and right to much on hard acceleration

still tinkering with different setups, if you have anything worthwhile to add to the discussion

This is a bit pedantic at this point but

Nah man, go back and read the thread again. I wasn't the one to start posting dragy runs

I didn't say otherwise - I said you were the one to begin comparing draggy results of the one that posted, to other results you said you found on your own (2 European based shops). My statement simply was, it's rather useless comparing these. If you still want to, cool. Especially if you're running a tire that is that much different from stock rolling diameter, as you've dropped your revolutions per mile by a fair amount and increased circumference. All of this should be taken into account if you're comparing any data that involves time and speed, as you've now changing the effective final drive ratio (down to 3.22, vs stock 3.317). 285/30/22 would be your closest to an oem rolling diameter, and it's what the 22 inch equipped cars use. 295/30 is also awfully close, only differing from stock rolling diameter by a very small amount.

I also haven't misunderstood anything about the rear wheel steering weight. I've been working with unitronic all year on tuning my car. It's in my email, in writing. Whether those guys are right also isn't any of my concern

You brought this into the mix. I wasn't the one to say it can't be had without rear wheel steering, someone else did, within the last few days. I simply said, and said it for the first time 30 minutes ago, that in the US, they come with it as standard. It can't be had any other way. I also know, as I worked for Audi for many years, that it doesn't weight 1200 lbs. It may not even weigh 120 lbs in total. Just look up base curb weight of a European RS6, and compare it to base curb weight of a US spec one. There isn't a 1200 lbs difference....that doesn't even follow any sort of logic. No goalpost was moved, simply stating a fact so others don't get confused.

As far as tire pressures, the same way one does it at a track day, would generally hold true for the street. Tire temp and chalk. The thing is though, unless you're only on the same roads day in day out, it will take constant adjustment. Especially this time of year where temps can go to dead cold one day, and in the 50's the next. If outright overall balance is what you want, between launching, cornering, braking, and handling day to day events, while keeping your wheels intact, start with the stock suggested pressure in the door jam, and adjust. My guess is you will end up within a few lbs of that, but nothing too dramatic. One DOT full tread tire isn't going to differ greatly from another at the end of the day. For pure drag strip use, different story. I have found most cars wanted significantly lower than street pressures (often half). But this makes it very sloppy almost everywhere else, as the sidewalls alone aren't meant for those low pressures

[funclub@caseyha]

This is a bit pedantic at this point but



I didn't say otherwise - I said you were the one to begin comparing draggy results of the one that posted, to other results you said you found on your own (2 European based shops). My statement simply was, it's rather useless comparing these. If you still want to, cool. Especially if you're running a tire that is that much different from stock rolling diameter, as you've dropped your revolutions per mile by a fair amount and increased circumference. All of this should be taken into account if you're comparing any data that involves time and speed, as you've now changing the effective final drive ratio (down to 3.22, vs stock 3.317). 285/30/22 would be your closest to an oem rolling diameter, and it's what the 22 inch equipped cars use. 295/30 is also awfully close, only differing from stock rolling diameter by a very small amount.



You brought this into the mix. I wasn't the one to say it can't be had without rear wheel steering, someone else did, within the last few days. I simply said, and said it for the first time 30 minutes ago, that in the US, they come with it as standard. It can't be had any other way. I also know, as I worked for Audi for many years, that it doesn't weight 1200 lbs. It may not even weigh 120 lbs in total. Just look up base curb weight of a European RS6, and compare it to base curb weight of a US spec one. There isn't a 1200 lbs difference....that doesn't even follow any sort of logic. No goalpost was moved, simply stating a fact so others don't get confused.

As far as tire pressures, the same way one does it at a track day, would generally hold true for the street. Tire temp and chalk. The thing is though, unless you're only on the same roads day in day out, it will take constant adjustment. Especially this time of year where temps can go to dead cold one day, and in the 50's the next. If outright overall balance is what you want, between launching, cornering, braking, and handling day to day events, while keeping your wheels intact, start with the stock suggested pressure in the door jam, and adjust. My guess is you will end up within a few lbs of that, but nothing too dramatic. One DOT full tread tire isn't going to differ greatly from another at the end of the day. For pure drag strip use, different story. I have found most cars wanted significantly lower than street pressures (often half). But this makes it very sloppy almost everywhere else, as the sidewalls alone aren't meant for those low pressures

The sticker on my door jam was set for max psi for the wheels instead of optimal weight

I originally had the stock 285/30 22s and swapped to the 315s

So I, tried to go by load indexes for the wheels based on axel weight at first but the load rates for a 315 essentially start capping at 35psi for for any psi of the OEM tire over 39psi so it wasn't really giving me a lot to work with

So I moved to chalk and found that with a 315 on the car that I can drop the psi to essentially flat tire range (22 psi) without the chalk affecting the side wall because the side walls on the 315/30 22s are very stiff. Figured that was still not good for the tire long term so I hopped in here to get some feedback on what others with the same or comparable wheel specs have been running

Then I went to VIR and hit the track and learned first hand that 32psi hot is too little to stay off the side wall but it's pretty close

Took the car cross country with a full load, based on wear I can say that 48 PSI hot is too much with them even under full load

So I've went back to the load indexes and have started playing around with a few staggered set ups between 32psi to 39 psi cold since that seems to be getting closer to Goldie locks zone

running 39/32 cold seems to work well on the streets around here however I'm going to play around with a few more spots and see if the car performs better or worse now that I have a benchmark I like